The invention relates generally to electronic amplifier circuits, and more specifically to use of negative hysteresis to create a low jitter amplifier.
Electronic circuits, including digital circuits used in modern computers and other digital electronic devices, commonly employ differential amplifiers or comparators to provide an output indicating which of two inputs is of a greater electrical potential. As the name comparator implies, the comparator or differential amplifier in effect compares the two input signals, and indicates which of the inputs is greater in value.
Such devices often bear significant resemblance to operational amplifiers, except that a comparator is specially designed to operate such that the output is either a positive value or negative value, with no linear range in between. This can be implemented with high gain differential amplifier circuits such as are normally employed in operational amplifiers, which are sometimes used in open loop mode (no feedback) as comparators.
These comparator or differential amplifier circuits are often employed in circuits such as analog-to-digital converters, where an analog input signal is compared to a known reference voltage to digitally approximate the analog value of the input signal. Other applications for comparators exist in digital circuits, where they are used as input buffers or receivers for digital data. In this mode, the comparator assures that a received signal that may contain noise or other voltage variations is propagated locally from the comparator as either a logical positive or negative value. Unwanted variations in voltage may include in some circumstances noise from conducted or electromagnetic interference, slow transitions between positive and negative states due to reactance of the transmission medium, and other sources of undesired voltage variation in the signal.
Where slow transitions occur between positive and negative states, it will usually take longer for the transition to be detected by the comparator than is desirable because the reference voltage to which the incoming signal is compared is usually set to a reference value half-way between the positive signal voltage level and the negative signal voltage level. This both provides relatively high immunity against false switching from voltage noise, and equalizes the response time for transitions from positive to negative levels with transitions from negative to positive levels. If this reference voltage is adjusted closer to one signal voltage level than the other it will speed up detection of transitions from that level to the other, but will significantly slow down detection of transitions in the opposite direction.
What is desired is a simple comparator circuit that provide the ability to more quickly detect transitions from one voltage signal level to a second voltage signal level without negatively impacting the ability to quickly detect transitions occurring in the opposite direction.